Toxicity Characteristic Leaching Procedure Research Articles

Feasibility and Environmental Compatibility of Concrete using Chromium Bearing Wastewater

The effluents of chrome plating industry seepage contain toxic hexavalent chromium generally in the range of 100 to 300 mg/L. The said values of chromium are not advisable to dispose to surface water bodies or land and the treatment process of this wastewater is quite expensive. Herein, we found a course of action to reuse the wastewater in cement matrix in manufacturing concrete work. The M-30 grade concrete samples were casted with portland slag cement (PSC) at wastewater to binder ratio of 0.45. The technical compatibility of concrete specimen i.e. the chromium immobilization and other properties are well satisfied nevertheless a small decrease in hardened concrete values also observed. XRD study revealed that the hydration product Ca(OH)2 is replaced by more insoluble CaCrO4. Scanning electron microscopy study (SEM) with energy dispersive spectrum (EDS) study exhibited the immobilization of chromium and quantification of chromium content. The mortar samples from concrete after 56 days of air curing were subjected to toxicity characteristic leaching procedure (TCLP) test at pH 2.88. In addition, two days’ short tank leaching test was conducted with the concrete samples as a whole. The leachability of toxic Cr6+ found in the range 0.03-0.09 mg/L and the total chromium (TCr) values in the range 0.12 -0.17 mg/L, which are less than discharge standard as per EP Act (1986), India. All these leaching test results comply with the discharge norms to land and inland surface water, respectively. Thus, the concrete specimens using aforesaid wastewater satisfy the technical aspects and fulfil the environmental requirement.

Remediation Efficiency of the In Situ Vitrification Method at an Unidentified-Waste and Groundwater Treatment Site

The subject of this study was the dust collected from an electric arc furnace at an unidentified-waste treatment site in southern Taiwan. The dust underwent an in situ vitrification (ISV) process and was tested using the toxicity characteristic leaching procedure (TCLP), at the end of which the final product was analyzed for its stability and weather resistance. This study then examined the above results to determine whether the ISV process helps to enhance the efficiency and economic benefits of said waste-treatment site. A TCLP test conducted on the dust that had been treated with ISV revealed that concentrations of various heavy metals were not only far below those of the unprocessed sample dust but also fell below the limit stipulated in the TCLP regulation of Taiwan’s Environmental Protection Administration. The results show that after undergoing ISV treatment, heavy metals in the dust were either encapsulated or bound in silicon lattices and thus barely leached from the dust. Analyses using scanning electron microscopy (SEM) and an energy dispersive spectrometry (EDS) indicate that the surface of the dust appeared more compacted after going through the ISV process. In addition, the highly contaminated dust that underwent ISV treatment saw a pronounced decrease in or elimination of wave crests. Another analysis applying X-ray diffraction (XRD) showed that the SiO2 crests disappeared in the processed dust, suggesting that the crystal structure was replaced with quasi-vitreous products after ISV treatment. In the event that pollutants were extant, they were usually characterized by smaller size, high stability, excellent weather resistance, an innocuous nature, and recyclability.

Immobilization of vanadium and nickel in spent fluid catalytic cracking (SFCC) catalysts-based geopolymer

In recent years, the use of spent fluid catalytic cracking (SFCC) catalysts to prepare geopolymers has received attention from academic and industrial circles. However, SFCC catalysts have been classified as hazardous waste in China due to their vanadium and nickel content. In this paper, the immobilization rates of vanadium and nickel in geopolymers prepared with SFCC catalysts were studied through a toxicity characteristic leaching procedure (TCLP). The immobilization mechanism of nickel and vanadium during geopolymerization was investigated by XPS, SEM, XRD, and compressive strength measurements. The nickel and vanadium TCLP concentrations of the SFCC catalyst-based geopolymer are 0.032 mg/L and 10.63 mg/L, respectively. Nickel in the SFCC catalyst is partly dissolved and adsorbed by the negatively charged tetrahedral aluminum in the geopolymer. However, because vanadates formed under alkaline conditions are negatively charged and readily soluble in water, vanadium in the SFCC catalyst is neither immobilized by the charge balance nor effectively immobilized by physical encapsulation. Therefore, the use of SFCC catalysts to prepare geopolymers will lead to vanadium contamination in the environment. In order to clarify the maximum vanadium content in SFCC catalysts for preparing geopolymers without environmental risk, SFCC catalysts with different vanadium levels were prepared by leaching. It was concluded that when the vanadium content in the SFCC catalyst is lower than 1861.4 mg/kg, the vanadium content in the leachate is lower than 2 mg/L and the geopolymer can be considered a non-hazardous material.

A stepwise microwave synergistic pyrolysis approach to produce sludge-based biochars: Optimizing and mechanism of heavy metals immobilization

A technical approach of stepwise microwave synergistic pyrolysis (SMSP) had been proposed to produce value-added sludge-based biochar. The approach includes a conventional pre-pyrolytic stage and a sequential microwave pyrolysis stage. It is vital to adjust conventional pre-pyrolysis parameters (i.e. temperature and time) to improve immobilization effect of heavy metals and decrease toxicity of sludge-based biochar. In the paper, sludge-based biochars were generated from different pre-pyrolysis temperature (400 ∼ 700 °C) and time (5 ∼ 20 min) by the SMSP approach. For heavy metals (Cu, Zn, Ni, Pb) in biochars, residual ratio, leaching ratio, chemical fractions and ecotoxicity were measured by using microwave digestion method, toxicity characteristic leaching procedure (TCLP) method, modified european community bureau of reference (BCR) method and risk assessment code (RAC) method respectively. The results demonstrated that 600 ∼ 700 °C and 10 ∼ 20 min are more suitable pre-pyrolysis temperature and time for immobilization of heavy metals via vitrification. Heavy metals in optimum sludge-based biochar (SBC) would have high residual ratio, low leaching ratio and low ecotoxicity risk simultaneously. Residual ratio of heavy metals in SBC are about 15% higher than that in optimum conventional sludge-based biochar (CSC). And leaching ratio of heavy metals in SBC are about 60% lower than that in CSC. These are mainly attributed to the shortened pyrolysis time and the high-energy sites effect induced by microwave heating.

Physicomechanical properties, stabilization mechanism, and antifungal activity of alkali-activated slag mixed with Cr6+ and Ni2+ rich industrial wastewater

An eco-sustainable approach applied to full disposal of Ni and Cr (VI) wastewater through the fabrication of alkali-activated slag (AAS). The impact of activator type (NaOH, Na2SiO3, and NaAlO2), heavy metal-containing-wastewater (Ni or Cr), and curing time (1-90-day) on the compressive strength, drying shrinkage, and immobilization efficiency have been addressed. Both compressive strength gain and loss were detected when Cr- and Ni-wastewater was mixed with AAS, depending on the type of alkali-activator. Nevertheless, all activated mixtures with wastewater demonstrated drying shrinkage values lower than that of the control sample (mixed with tap water). Ni and Cr have stabilized inside AAS-microstructure through the cationic exchange between Mg/Ni and Cr/Al within hydrotalcite phase or their localization on a negative charge of tetrahedral Al atom inside activated aluminosilicate skeleton. All the fabricated samples showed Ni and Cr concentrations in leachates lower than the regularity limits of toxicity characteristic leaching procedure (TCLP) and solubility threshold limit concentration (STLC) after 28-day of curing. The proposed strategy not only successfully applied for the safe disposal of heavy metals but also led to the fabrication of cementitious materials with high resistivity to detrimental sulfur oxidizing Aspergillus Niger fungal strain, which makes such cement effectively applied in microorganisms-rich-media.

Remediation of As and Cd contaminated sediment by biochars: Accompanied with the change of microbial community

As and Cd pollution in sediment has posed a potential threat to ecosystem owing to their high toxicity. Fixing heavy metals and transforming their speciation into stable forms can be a sustainable method. In this study, nine biomass feedstocks were pyrolyzed into biochars for immobilization of As and Cd in sediment, and the accompanied changes in the microbial community were analyzed to evaluate their effect on bioavailability. The heavy metal immobilization capacity of biochars in sediment were assessed by measuring the change of As and Cd concentrations in aqueous phases (overlying water (COW) and pore water (CPW)) and the leachate of Toxicity Characteristic Leaching Procedure (TCLP), and metal speciation after biochar treatment. The maximum reduction of As and Cd concentrations could reach 95% and 78% (COW), 73% and 59% (CPW), 81% and 37% (leachate), respectively, and the F1, F2, F3 fraction (bioavailable form) of As and Cd significantly decreased (up to 18.0%) in the biochar-treated sediments. The ACE (Abundance-based Coverage Estimator) and Shannon index results revealed that biochars efficiently enriched the microbial biodiversity and population in the sediment. Water hyacinths biochar (WHB) exhibited the better performance among all biochar samples mainly due to the abundant oxygen-containing functional groups on the surface and the higher O/C. The overall results highlighted the inhibition effects of biochar on heavy metal mobility and bioavailability, and helped to provide guidance for optimization of biochars for sediment remediation.

Solidification/stabilization remediation of heavy metal from petroleum Al-Dura sludge with Portland cement

The aim of this research is to evaluate the method of stabilization/solidification in the treatment of cadmium and iron from Al-Dura Oil Refinery sludge. In addition, the effect of organic matter was studied by using treated and untreated sludge. The procedure was applied in three treatments, where the cement was added to a mixture of sludge/sand prepared at three ratios (i.e., 1:2, 1:3, and 1:4) and also without any sludge (as the control), with the treated and untreated sludge used in proportions of 7, 15, and 25% by weight of sand. Tests of unconfined compression strength and a toxicity characteristic leaching procedure were used to evaluate the stabilization/solidification matrix. The highest unconfined compression strength was 3 Mpa for the samples with untreated sludge, while it was 2.1Mpa for samples with treated sludge. However, the results of the leaching test showed that the samples with the untreated sludge had more retention efficiency compared to the samples with treated sludge. The cadmium retention efficiency was 99.1%, while for iron, it was 97.5%. The organic matter (especially aromatic) had no effect on the leaching of either Iron or cadmium. Therefore, this method seems to be highly successful in the treatment of both Iron and cadmium with untreated Al-Dura Oil Refinery sludge.

Valorization of fine fraction from legacy waste as fired bricks: A step towards circular economy

Old landfills and dumpsites, created due to a linear approach towards municipal solid waste (MSW) management, are one of the major environmental hazards, especially in developing countries. Around 50% of the dumped waste can be characterized as fine fraction (FF), making its recovery a vital parameter for achieving a circular economy. This study investigates the application of FF obtained from the Indian MSW dumpsite to replace topsoil used for fired brick production, which is one of the primary construction materials in India. The raw materials (FF and clay) were mixed in different proportions and fired at a temperature of 800–1000 °C. Physicochemical, mechanical and environmental properties were analyzed for fired bricks using standard methods. Results showed that the fired bricks produced from FF had low density and thermal conductivity than control bricks providing advantages over conventional bricks for transportation and energy savings. The compressive strength (CS) of the bricks increased with an increase in temperature and reduced with an increase in FF, suggesting only a certain amount of clay can be replaced. Hence further optimization using response surface modelling was carried out. The optimization results showed that clay could be substituted up to 23% at 1000 °C (CS = 37.5 N/mm2) by FF to meet Indian regulatory limits for CS. Toxicity characteristic leaching procedure test showed that fired bricks produced from FF are safe for application. The study shows that FF can substitute part of clay in fired brick production, which can help to curb topsoil exploitation while achieving a circular economy by bringing dumped FF back to the anthropogenic material cycle.

Combined amendment improves soil health and Brown rice quality in paddy soils moderately and highly Co-contaminated with Cd and As

In situ remediation technology applied aims to not only decrease cadmium (Cd) and arsenic (As) uptake by rice but also improve soil health and rice quality in contaminated paddy soils. Here the effects of a combined amendment, consisting of limestone, iron powder, silicon fertilizer, and calcium-magnesium-phosphate fertilizer, with three application rates (0, 450, and 900 g m−2) on soil health, rice root system, and brown rice quality were compared in moderately versus highly Cd and As co-contaminated paddy fields. After the amendment application, soil pH, cation exchange capacity, four kinds of soil enzyme activities increased (sucrase, urease, acid phosphatase, and catalase), and concentrations of leached Cd/As decreased, as measured by the DTPA (diethylene triamine pentaacetic acid) and TCLP (toxicity characteristic leaching procedure). Changes in the above soil indicators promoted soil health. In both fields, the dithionite-citrate-bicarbonate (DCB)-Fe and DCB-Mn concentration in iron plaque increased and root length became longer. Changes in the above root system indicators reduced the root system's absorption of Cd and As but increased that of nutrients. Under 900 g m−2 treatment, the Cd concentration in brown rice of two sites decreased by 55.8% and 28.9%, likewise inorganic As (iAs) decreased by 50.0% and 21.1%, whereas essential amino acids increased by 20.4% and 20.0%, respectively. Furthermore, the Cd and iAs concentrations in brown rice were <0.2 mg kg−1 (maximum contaminant level of Cd and iAs in the Chinese National Food Safety Standards GB2762-2017 for brown rice) under the 900 g m−2 in the moderately contaminated field. These results suggest the combined amendment can improve soil health and brown rice quality in the moderately and highly Cd- and As-co-contaminated paddy soils, offering potential eco-friendly and efficient remediation material for applications in such polluted paddy soils.

Long-term and high-bioavailable potentially toxic elements (PTEs) strongly influence the microbiota in electroplating sites

Multiple potentially toxic elements (PTEs) wastes are produced in the process of electroplating, which pollute the surrounding soils. However, the priority pollutants and critical risk factors in electroplating sites are still unclear. Hence, a typical demolished electroplating site (operation for 31 years) in the Yangtze River Delta was investigated. Results showed that the soil was severely polluted by Cr(VI) (1711.3 mg kg−1), Ni (6754.0 mg kg−1) and Pb (2784.4 mg kg−1). The spatial distribution of soil PTEs performed by ArcGIS illustrated that the soil pollution varied with plating workshops. Hard Cr electroplating workshops (HCE), decorative Cr electroplating workshops (DCE) and sludge storage station (SS) were the hot spots in the site. Besides, the toxicity characteristic leaching procedure (TCLP) - extractable Cr and Ni contents in different workshops were significantly related (P < 0.05) to their bioavailable fractions (exchangeable fraction (F1) + bound to carbonate fraction (F2)), which pose potential risk to humans. Although the soil total Pb concentration was high, its mobility was very low (<0.007%). Moreover, the soil microbial community dynamics under the stress of long term and high contents of PTEs were further revealed. The soil microbiota was significantly disturbed by long term and high concentration of PTEs. A bit of bacteria (Caulobacter) and fungi (Cladosporium and Monocillium) showed tolerance potential to multiple metals. Furthermore, the canonical correspondence analysis (CCA) showed that the bioavailable fractions (F1 + F2) of Cr and Ni were the most critical environmental variables affecting microbiota. Therefore, remediation strategies are required urgently to reduce the bioavailability of soil Cr and Ni. The results of this study provide an overview of the pollution distribution and microbial dynamics of a typical plating site, laying a foundation for ecological remediation of electroplating sites in Yangtze River Delta of China.

Mechanical, durability properties, and environmental assessment of geopolymer mortars containing waste foundry sand

Today, with the expansion of industries and construction activities, attention to environmental issues such as sustainable development, recycling, reuse, etc. becomes important. The global demand for cement production has been increasing. One ton of cement releases about one ton of carbon dioxide into the atmosphere. Also, after freshwater, sand is considered the second natural resource that is consumed.Due to the limited sand resources and the concerns around the environmental issues of cement production, in this study, the use of waste foundry sand (WFS) as an alternative to aggregate in slag-based geopolymer mortars as an alternative to cement has been considered. WFS is a by-product of the foundry industry, which is produced in large quantities and buried in landfills, and slag is the by-product of iron and steel making process which is highly cementitious and high in calcium silicate hydrates (CSH).In this study, the mechanical, durability properties, and environmental assessment of geopolymer mortars using WFS were investigated. The results show that the compressive strength of geopolymer mortars containing treated WFS at the age of 91days had an increase of 158% compared to cement-based mortars. The adhesion and flexural strength in geopolymer mortars containing treated WFS compared to untreated mortars increased by 145% and 18%, respectively. Toxicity characteristic leaching procedure (TCLP) results showed that the concentration of heavy metals in the leachate WFS, mortars containing treated and untreated WFS, and ground granulated blast-furnace (GGBF) slag was within the standard permitted limitations and WFS is not a hazardous waste.

Effect of cement kiln dust, lime and fly ash on metal leaching characteristics of oil sands tailings from Alberta, Canada

The oil sands industry of Alberta generates huge amounts of tailings in a slurry form that typically require up to 40 years to consolidate in very large tailings ponds which are up to 150 m in height. Cement kiln dust (CKD), a byproduct of the ordinary Portland cement manufacturing process, as well as lime and fly ash, collectively referred to as geopolymers, may have the potential to reduce the tailings slurry consolidation period from 40 years, thus affecting the sustainability of such tailings facilities. However, first, it must be demonstrated that these geopolymers will also decrease the metal leaching from thickened tailings (TT) and mature fine tailings (MFT) from the oil sands industry. This study was focused on the use of geopolymers to reduce the environmental impact of TT- and MFT-tailings in the Alberta oil sands industry. Toxicity characteristics leaching procedure (TCLP) and static leaching test (SLT) was used to examine the leaching of metals from tailings, with the SLT test effectively mimicking the leaching process in the tailings ponds environment. Under non-acidic conditions corresponding to the SLT test results, iron concentrations with values of about 530-705 ppm were found to be lower than previous studies on oil sand tailing ponds (2400 ppm). Results showed that geopolymer amendment of TT and MFT significantly reduced the leaching of heavy metals. SLT tests showed that amendment of MFT with 7% CKD decreased Pb, Mn, and Fe leaching, whereas TT-amended with 4% CKD decreased Cu, Pb, Zn, Mn, and Fe. Overall, the CKD amendment of TT showed more than 95% efficiency in the reduction of leaching of all heavy metals. In TCLP tests, TT-amended with 2% FA decreased the leaching of Pb and Ni to acceptable levels with substantial efficiency in reducing the leaching of Fe, Cu, and Zn. TCLP tests also showed that among different amendments, TT-amended with 4% CKD or 2% FA were the most effective proportions for controlling metal leaching from TT, while MFT-amended with 7% lime/FA or 3% CKD were the effective proportions for reducing metal leaching from MFT. Thus, it is deduced that CKD at 3%-4% w/w amendment would work best for reducing leachate levels of both TT and MFT. While amendment of tailings by means of a combination of fly ash and lime also were effective in reducing the leaching of metals, these two geopolymers were not as effective as the CKD amendment.

Stabilization of liming sludge in brick production: A way to reduce pollution in tannery

In leather processing, hair burning liming operation is employed to remove the hair/wool, epidermis, fat, grease, and non-structural proteins. The discharged wastewater from the hair burning step produces the most of the sludge in the tannery which is a hazardous waste that has a serious impact on the environment. Thus, managing of the liming sludge has become a great challenge for the leather industry. Using liming sludge as a raw material in building materials has the potential to reduce environmental pollution. In this novel work, building bricks were made under field conditions, where liming sludge (w/w) were incorporated by 2%, 4%, 6%, 8%, 10%, and 12%, and fired in a kiln at 1000 °C. Results reveal that 6% liming sludge incorporated fired brick showed the best engineering properties, microstructure, and chemical characteristics. It also offered the best properties such as compressive strength (ASTM C 67-02c), area shrinkage (ASTM C326), weight loss, bulk density, and water absorption (ASTM C373-88) which were found to be 27.50 MPa, 5.03%, 7.79%, 2.18 g/cm3, and 10.46%, respectively. Moreover, Fourier-Transform Infrared (FT-IR) spectroscopy and Scanning Electron Microscope (SEM) analysis showed that liming sludge content has a profound effect on the structure of fired bricks. The Netherlands tank (NEN 7345) and Toxicity Characteristic Leaching Procedure (TCLP) (USEPA 1311) leaching test results exhibited insignificant leachability of metals from the sludge incorporated fired bricks. Hence, the utilization of liming sludge as an ingredient for producing construction materials will reduce the pollution loads of tannery industries.

Compressive Strength and Leaching Characteristic of Geopolymer Composite from Coal Fly Ash and Nickel Laterite Mine Spoils

Geopolymer, also referred to as “alkali-activated material” or “zeocement”, is an emerging sustainable material to replace Portland cement-based binder. It requires a straightforward process and has the potential for large-scale waste valorisation and utilisation and a lower carbon footprint. Several aluminosilicate materials as geopolymer precursors have been explored, such as coal fly ash and metakaolin, among others. However, the characteristics of raw materials vary depending on the source. Hence, this study aims to synthesise geopolymer composite from raw materials that are available locally. Coal fly ash and nickel laterite mine spoils were explored as a potential geopolymer precursor. Optimal mix formulation of 50 % nickel laterite mine spoils / 50 % coal fly ash, sodium hydroxide to sodium silicate ratio of 1:2, and activator to precursor ratio of 0.44:1 yielded a 28 d compressive strength of 22.1 ± 4.4 MPa and a 180 d compressive strength of 32.3 ± 7.4 MPa. The result implies that this eco-friendly geopolymer material can be potentially used for pedestrian pavers, light traffic pavers, and plain concrete for levelling and structural applications. Before any field-scale application, investigating the leachability of material is imperative. Hence, the toxicity characteristic leaching procedure (TCLP) was employed to evaluate the leachability behaviour of both the raw materials and developed geopolymer composite in this study. The results revealed that the concentration of the trace metals released pose no significant environmental and leaching hazard into the soil, surface, and groundwater sources based on the threshold limit as defined by USEPA.

Desorption and Migration Behavior of Beryllium from Contaminated Soils: Insights for Risk-Based Management.

Factors influencing the desorption, distribution, and vertical migration behavior of Be in contaminated soils are not fully understood. This study examined the desorption and migration of Be in a soil profile from a legacy radioactive waste disposal site using different batch leaching [monofilled waste extraction procedure (MWEP); synthetic precipitation leaching procedure (SPLP); simulated acid rain solution (SARS); and toxicity characteristic leaching procedure] and sequential leaching [community bureau of reference (BCR)] methods for insights relevant to the application of risk-based management. The results showed that Be desorption was higher in the presence of organic than the inorganic leachate composition (MWEP < SPLP < SARS < TCLP < BCR first-step). The desorption followed three diffusion control mechanisms, which resulted in three desorption rate constant estimates of 157, 87.1, and 40.4 Be/kg.h0.5, and the estimated desorption maximum was 556 μg/kg. The desorption process was, spontaneous (ΔG > 0), enthalpically and entropically influenced. Increasing the incubation period and heat treatment resulted in a decrease of Be desorption and migration. The soil clay content and pH were the primary factors influencing Be desorption, and the results suggested that Be was desorbed from metal oxyhydroxides and surfaces of silicates (e.g., reactive surfaces of clay minerals), organic matters, and soil pores. Because of high Kd values, the mobility of Be was limited, and no exceedances of ecological or human health risk index or guidelines were determined for the current contamination levels at the site. However, Be released from the waste trenches has the ongoing potential to increase Be concentration in the soil.

The Influence of Aluminum Slag Ash for Paving Block Production

Aluminum slag ash commonly used as road and river embankments. It had disposed in an open site and potentially increase ammonia, sodium, potassium, chloride and total dissolved solids levels in the surrounding environment. As much as 90% of Portland cement is composed of a mixture of elements of Ca, Si, Al, and Fe which are bonded into certain complex compounds. This study aims to analyze the influence of cement substitution with aluminum slag ash on the compressive strength and water absorption capacity of the paving block, and the appropriate type of paving block quality which is following SNI 03-0691-1996. The test objects used were paving blocks with a ratio of cement and sand of 1:3, where the composition of the addition of aluminum slag ash used was 5%; 10%; 15%; and 20%. The tests in this study were on compressive strength, water absorption capacity, and Toxicity Characteristic Leaching Procedure (TCLP) tests. The optimum composition is 10% aluminum slag ash in cement substitution. The type of quality is category B paving for parking equipment. The results of the TCLP on a 10% composition paving obtained that the parameter concentration is below the TCLP quality standard.

Determination of extractable fluorine from residue of oil and gas industry by HR-CS MAS applying toxicity characteristic leaching procedure

Toxicity characteristic leaching procedure (TCLP) is a standard extraction procedure in acetic acid medium for toxicity assessment. Fluoride (F−) is one of the extracted forms of fluorine monitored that has a regulated value. In this study, the CaF molecule was used to determine the leached fluorine (F) (in acetic acid medium, at pH 2.88 and 4.93) of residues from the oil and gas industry. The thermal stability of the CaF molecule and the stoichiometric ratio Ca:F for the formation of the molecule were evaluated at the wavelength (λ) 606.4322 nm. The results demonstrated that the CaF is thermally stable, enabling the use of temperatures of 1000 and 2300 °C for pyrolysis and vaporization, respectively. The proposed method allows calibration against aqueous standards to determine the extracted F concentration in leachate extracts, low limit of detection (0.01 mg L−1) and good precision (RSD ≤ 5%). Evaluation of the stability of extracted F in the leachate extracts found that, under the evaluated conditions, the analyte remained stable for up to 21 days after the TCLP procedure. The extracted F concentration obtained in the leachate extracts ranged from 0.520 ± 0.002 to 1.18 ± 0.04 mg L−1 for pH 2.88 and from 0.149 ± 0.001 to 0.574 ± 0.004 mg L−1 at pH 4.93. Hence, all samples analyzed showed an extracted F concentration below 150.0 mg L−1 and were not classified as toxic considering this parameter.

Effect of a Passivator Synthesized by Wastes of Iron Tailings and Biomass on the Leachability of Cd/Pb and Safety of Pak Choi (Brassica chinensis L.) in Contaminated Soil

Cadmium (Cd) and lead (Pb) carry a high heavy-metal-toxic risk for both animals and plants in soil. In this study, iron-based biochar (T-BC) was prepared by co-pyrolysis using wastes of iron tailings and biomass with urea as the functioning agents. Field-emission scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and toxicity-characteristic leaching procedure (TCLP) methods were employed to analyze the physicochemical characteristics of T-BC. Additionally, a pot trial was conducted to examine the effects of T-BC on the physiological characteristics of pak choi (Brassica campestris L.), the availability of heavy metals, and enzyme activities in the soils. The results show that toxic metals have been volatilized by the roasting process and immobilized within T-BC via the formation of stable metal-compounds during the co-pyrolysis process, which satisfies the requirements of a soil passivator. Incubation experiments showed that the DTPA-extractable Cd and Pb in contaminated soils decreased with an increasing amendment rate. Moreover, in the pot experiments, by adding 1% (w/w) T-BC into soils, the soils benefited from its large adsorption, complex precipitation, and immobilization capacity. Approximately 36% Cd and 29% Pb concentrations of edible parts in pak choi were reduced. The amendment proved promising for the stabilization of Cd and Pb in contaminated soils, while providing a strategy for solving the residual waste of tailings and biomass.

Investigation of Metal and Trace Elements of Cenospheres from Lignite High-Calcium Fly Ash (Thailand)

High-calcium fly ashes contain a large content of small particles including cenospheres of chemical constituents known to be similar to fly ash and the parent coal. Coal fly ash contains metal and trace elements that may leach out during disposal or utilization. This work aimed to understand an overview of cenosphere characteristics relating to fly ash and leaching study. To our knowledge, this is the first report on metal and trace element leaching of cenospheres separated from high-calcium (28.9 wt.%) class C fly ash produced from the Mae Moh coal-fired thermal power plant in Thailand. In this study, the cenospheres were separated from fly ash by a wet separation process (sink-float method) using water as medium. Physical properties, morphology, chemical composition, the mineral phases of cenospheres and fly ash have been characterized. Extraction was carried out by acid digestion; the selected metal and trace elements in this study are Mg, Al, Zn, Pb, Cd, Cr, and Cu; the obtained environmentally available concentrations of cenospheres were analyzed in comparison to those of fly ash. The concentrations of Cu, Cr, Pb, and Cd elements of interest in the leachates obtained from the toxicity characteristic leaching procedure (TCLP) showed the tendency to decrease in that order. All the elements were found below the permissible limit values regarding Thailand soil quality standards. Association of the heavy metal trace elements in cenospheres and fly ash was discussed in in terms of physico-chemical-geochemistry correlating with the leaching concentrations.

Combined effects of Penicillium oxalicum and tricalcium phosphate on lead immobilization: Performance, mechanisms and stabilities

Phosphorus (P) containing minerals are identified as effective Pb stabilizers in soil, while their low solubility limit the Pb immobilization efficiency. In this work, the combination of phosphate solubilizing fungi (PSF) Penicillium oxalicum and tricalcium phosphate (TCP) was constructed and applied to improve Pb immobilization stabilities in medium and soils. P. oxalicum+ TCP could significantly improve Pb2+ removal to above 99% under different TCP/Pb2+ and pH values. TCP and P. oxalicum could remarkably immobilize Pb by ion exchange, and PbC2O4 precipitation or surface adsorption, respectively. While the enhanced Pb immobilization in P. oxalicum+ TCP was explained by stronger Pb2+ interaction with tryptophan protein-like substances in extracellular polymeric substance, and the formation of the most stable Pb-phosphate compound hydroxypyromorphite (Pb5(PO4)3OH). Toxicity characteristic leaching procedure test showed that only 0.91% of Pb2+ was leachable in P. oxalicum+ TCP treatment, significantly lower than that in P. oxalicum (2.90%) and TCP (7.52%) treatments. In addition, the lowest soil exchangeable Pb fraction (37.1%) and the highest available soil P (88.0 mg/kg) were both found in P. oxalicum+ TCP treatment. By synergistically forming stable Pb-containing products, thus the combination of PSF and P minerals could significantly improve Pb2+ immobilization and stability in soils.